How does it come that you encounter this problem of dissonnance only in bar 22? How did you transcribe the first bars at the beginning of the secound part?

**The solution is very simple: in the entry part the voices are set for Bb clarinet, in the 2nd part they have to use A clarinets. That means: both instruments (clar. & trp.) play the same voice.**

Comment to your answers below:
Are you doing the transcription with a computer program a) or by hand b) ? In the first case it must have sounded the same dissonant as in bar 22 if you did it correct (considering there were Bb clarinets, as the clar, and trp). Play in unison from the beginning ... and as you transposed the Bb clar. a secound  up and the A trp. a small third up there must always have been a small second. the C played by a Bb clarinet doesn‘t sound as a B it is actually a Bb (flat)